The present invention relates to a method of synchronizing clocks in a bus type network, such as Ethernet, in which a number of nodes containing said clocks are connected to a common data channel. The invention also relates to a system of synchronizing clocks contained in a bus type local network, such as Ethernet, comprising a number of node equipments connected to a common data channel, each node equipment comprising an operating unit in the shape of a coupling unit and possibly further operating units, one of the node equipments being a synchronizing master, the master node, and the further node equipments being the slave nodes. In this context by node is meant on one hand the point of intersection itself between the data channel and the equipment coupled to the node and on the other hand the point of intersection inclusive of the equipment coupled to the node. The word "node" in the last mentioned meaning is also called "node equipment" in the following.
In local nets having a channel common to a multiplicity of nodes, e.g. of Ethernet type, the requirements until now on the synchronizing of the clocks in node equipment connected to the data channel have not been very high. For example, it has been possible to transmit information about the clock times of the nodes between the nodes as normal data messages. However, the transmit time of a data message varies to a great extent. Due to the fact that a multiplicity of nodes are connected to a common data channel, the data channel may be engaged with a transmission of other data messages and the data message containing the clock time is then forced to wait in a transmitter queue. When the data message containing the clock time reaches the receiving nodes the transmitted clock time is thus often inadequate. Until now it only has been possible to use such a net in applications in which the synchronizing between the nodes is not critical. However, strong desires exist to be able to use local networks having a common channel even in applications demanding a more accurate synchronizing, such as defense applications. One reason for this is the saving of space obtained by using a common data channel instead of a lot of separate connections. Another reason is the aspect of cost due to the fact that a common channel simplifies and cheapens the installation.